Symmetric Castling to either side (Players must agree before the game which type of castling [short or long] will they use in the game)
In a 10x8 setup castling can be either short (O-O) or long (O-O-O), but not both:
O-Ob is Kb1 & Rc1 [Kb8 & Rc8 for black]; or O-Oi which is Ki1 & Rh1 [Ki8 & Rh8 for black]
O-O-Oc is Kc1 & Rd1 [Kc8 & Rd8 for black]; or O-O-Oh which is Kh1 & Rg1 [Kh8 & Rg8 for black]
The Bishop Adjustment Rule giving players the choice (if they want) to change one of the Bishops to the opposite color squares in those setups where the Bishops start off on the same color.
Here is another 10x8 variant option for your engines, a random setup with the Four 'Modern' Chess Principles:
There are 151,200 possible starting positions!
The Four 'Modern' Chess Principles are:
In a 10x8 setup castling can be either short (O-O) or long (O-O-O), but not both:- O-Ob is Kb1 & Rc1 [Kb8 & Rc8 for black]; or O-Oi which is Ki1 & Rh1 [Ki8 & Rh8 for black]
- O-O-Oc is Kc1 & Rd1 [Kc8 & Rd8 for black]; or O-O-Oh which is Kh1 & Rg1 [Kh8 & Rg8 for black]
Here is a sample preset for 'Modern Capablanca Random Chess'.
PS-I submited the comment below on the subject of the Four Modern Chess Principles. The comment below can be deleted.